Conveyors are continuous moving belts that transport bulk and granular materials from one place to another. In some types of conveyors, the material travels on the belt itself. In other types of conveyors, buckets or flights are attached to the moving belt. An example of the latter type is a conveyor chain in which the belt is formed of multiple chain links, some or all of which contain flights. As the conveyor chain moves along inside an enclosed duct, the flights pull a cross-section of material along with it. Two links of a conventional fork link conveyor chain are shown in FIG. 1. The direction of travel of the conveyor chain is from right to left. Each link consists of a longitudinal portion with a leading end (commonly known as the head) that contains a opening and a trailing end that contains a bracket. The leading edge of one link fits within the bracket of the link ahead of it. The two links are secured together with a pin or other suitable fastener. Each link contains two opposed flights that are perpendicular to the longitudinal portion. Conveyor chain links are typically made of hardened steel.
As the conveyor chain travels along the duct, sparks are sometimes created from the metal-to-metal contact between the flights and the floor of the duct. In the grain industry, sparks can ignite grain dust explosions. Awareness of the danger of grain dust explosions ignited by conveyor chains has increased in the last few years. As a result, the grain industry has taken various steps to modify conveyor chains to reduce the chances of sparks.
A first modification has been to use links that are made totally of a polymeric material. Contact between the polymeric material and the metal ductwork does not cause sparks. For example, GEFA Ltd. of the United Kingdom produces GEFLEX acetal copolymer links. Unfortunately, the polymeric links are much more expensive than steel links and they are not nearly as strong. Furthermore, the flights wear much more rapidly than steel flights. When the flights are worn, the entire link must be replaced.
A second modification is to use steel links having a polymeric paddle attached onto a metal flight as shown in FIG. 2. When the polymeric paddle becomes worn, only the paddle itself needs to be replaced. John King Chains Company of the United Kingdom produces fork links having polymeric flights. However, worn polymeric paddles do not always get replaced when needed. As a result, the metal flight can become exposed and the danger of sparks again becomes present.
A third modification is to use steel links whose flights are made completely of a polymeric material as shown in FIG. 3. This modification retains the strength and durability of the steel links while reducing the danger of sparks caused by metal flights contacting the ductwork. Holes are drilled completely through the links. Polymeric flights having a base with mounting holes are then attached to the steel links with fasteners that pass through the flights and the link. The polymeric flights are easily replaced when worn. Unfortunately, drilling holes through hardened steel links is a slow and expensive procedure.
Accordingly, a demand exists for an improved method of producing steel conveyor chains having polymeric flights.